Target-type pilot burner



Nov. 3, 1964 w. F. JACKSON ETAL 3,155,143

TARGET-TYPE PILOT BURNER Filed Sept. 28, 1961 FIGS United States Patent 3,155,143 TARGET-TYPE PILT BURNER Wilbur F. Jackson, Rolling Hills Estates, and Edward E.

Schafer, Lynwood, Calif., assignors to Robertshaw Controls Company, Richmond, Va., a corporation of Delaware Filed Sept. 28, 1961, Ser. No. 141,332 2 Claims. (Cl. 158-113) This invention relates to improvements in pilot burners, and more particularly to pilot burners employed in environments where dust and lint are encountered in the combustion air.

In general, pilot burners employed in environments where air in the locality of operation is heavily laden with dust `and lint are usually of a non-aerated type of pilot. A familiar example of a pilot of this type is the target type pilot which employs no primary air intake and relies entirely upon secondary air injection directly into the cornbustion Zone. The target type pilot is substantially unaffected by lint or dust since the combustion air is injected directly into the combustion zone and there are no internal passages through which the combustion air must pass, thus eliminating any possibility of clogging of internal passages by lint or dust. These non-aerated or target type pilots have a generally high noise level due to `the high velocity impingement of the gas jet on the target and further have a tendency to blow at higher gas pressures. An aerated pilot, on the other hand, relies substantially entirely upon primary air injection and operates at a low noise level with little tendency toward blowing. In the usual case, the primary air intake of an aerated pilot designed for use in environments where dust and lint are encountered is constructed with a primary air intake so located that dust and lint particles will be incinerated by the pilot ame prior to their passage into the primary `air intake opening. However, regardless of the erhciency of incineration, such pilot will eventually become clogged with dust or lint particles with a corresponding loss in llame elfectiveness due to the reduction of the primary air intake which causes incomplete combustion.

It is a primary object of the invention to provide a pilot burner combining the advantages of both aerated and nonaerated pilots while eliminating the disadvantages outlined above.

It is another object of the invention to provide a pilot burner which will maintain a satisfactory pilot flame over a wide range of gas supply pressures.

It is another object of the invention to provide a pilot burner having a self-compensating primary air injection control over a wide range of gas supply pressures.

Stili another object of the invention is Ito provide a pilot burner normally operable with both primary and secondary air injection which will continue to operate upon the loss of all primary air.

The foregoing and other objects are achieved in a pilot burner in which both primary and secondary air are mixed with the fuel gas. A relatively open target hood construction permits suicient secondary air injection to maintain a pilot flame even in the absence of primary air. The primary air inlet is located near the pilot flame in a relationship such that the llame exerts a self-regulating action responsive to gas supply pressure on primary air injection.

Other objects and features of the invention will become apparent by reference to the following speciicationand to the drawings.

In the drawings:

FIG. l is a side elevational View, partially in cross section, of a pilot assembly including one form of pilot hood embodying the invention;

FIG. 2 is an elevational View of a sheet metal blank from which the pilot hood of FIG. 1 is formed;

FIG. 3 is a detail front view of a pilot hood of FIG. 1;

FIG. 4 is a cross sectional view taken on line 4-4 of FIG. 3;

FIG. 5 is a front elevational View of another form of pilot hood; and

FIG. 6 is a front elevational View of still another form of pilot hood embodying the invention.

Referring first to FIG. l, a thermocouple-pilot assembly is disclosed which includes a mounting bracket designated generally 1G having upper and lower flanges 12. and 14 which are bored as shown to receive a thermocouple 16 of conventional construction, thermocouple 16 being held in place on bracket 10 as by a spring clip member 18 resiliently clipped to thermocouple 16 and upper ange 12. At the outer end of upper llange 12, an integral neck 2li is formed and externally threaded as shown to receive a coupling nut 22 which is employed to couple a gas supply line 24 to bracket 1Q. A ball sleeve 26 is slipped over the upper end of supply line 24 and is formed with inclined sections at its opposite ends adapted to be wedged by complementary inclined sections formed in the interior of coupling nut 22 and a flared l'lange 28 at the lower' end of an orifice spud 30 into a gas tight seal on line 24 upon tightening of nut 22. An orice 34 is bored in the upper end of spud 3l) to discharge gas under pressure from the interior of spud 3i) in an upwardly directed jet.

The pilot hood of an embodiment shown in FIGS. l through 4, inclusive is formed from a one-piece blank B of sheet metal initially formed in the shape disclosed in FIG. 2 blank B is subsequently formed in a manner such that the main body portion of blank B is shaped into an outer tubular member 36 and an inner tubular member 33, connected to each other by an intermediate web 40. At the lower end of outer member 36, a plurality of mounting tabs 42 are bent outwardly, and tabs 42 are received within a recess 44 spot faced into the upper surface of upper ilange 12 of bracket llt) in concentric relationship with the central passage through neck 20. Tabs 42 are spot welded to bracket 1l) to support the pilot hood assembly upon the bracket. The upper portion of blank B is formed with side llanges 46 which extend along opposite sides of a forwardly inclined target portion 48 which, as best seen in FIG. 1, is inclined forwardly to overlie the upper ends of the inner and outer tubular members 38 and 36. The forward end of target 4S is formed with a horizontal lip 49 which assists in the self compensating flame action described below.

As best seen in FIG. 1, tubular members 36 and 38 are open at each end and the upper ends of both members are located at substantially the same level. The lower end 50 of inner member 38 is spaced upwardly above the lower end of outer member 36 so that when the pilot hood is mounted upon bracket 10 as shown in FIG. 1, the lower end of inner member 33 is spaced above orice 34.

When gas under pressure is supplie-d through supply conduit 24, the gas issues from oriiice 34 in an upwardly directed jet. Inner member 38 is oriented relative to orice 34 in a fashion such that the jet passes directly into the interior of inner member 38. The high velocity of the gas jet issuing from orice 34 causes areduction in pressure in the lower portion of outer member 36- i.e., that inte-rior portion of outer member 36 below lower end 50 of inner member SaS-and this local reduction of pressure inspirates a flow of air from the upper end of outer member 36 downwardly through the space between outer member 36 and inner member 3b. The inspirated flow of air pro-vides primary .air for mixture with the gas jet, this mixture being accomplished by the entrainment of air with the gas jet and the turbulence of flow of the gas and entrained air upwardly through inner member 38. The tendency of the gas jet to expand horizontally as it moves upwardly from orifice 34 causes impingement `of the jet against the inner side walls of member 3S to create the turbulence. However, the high jet velocity is suicient to discharge all of the gas issuing `from orifice 34 into the interior of member 38, the upward velocity of the jet being suflioient to prevent sidewards expansion of the jet radially beyond inner member 38 before the Vjet reaches lower end 50 of member 38.

' The action described` above is generally referred to as a primary air injection type 4of operation. In a primary air injection operation, is mixed with the gas at some point before the gas reache-s the zone or region of co-mbust-ion.Y In nthe struCIUi'eY disclosed, the llame Yor zone of combustion is located generally at the upper end of inner member 38. The structure disclosed in this application is especially devised to additionally provide for a secondary air injection. Secondary air injection is accomplished by injecting or mixing air with the combustion gas directly in the zone of combustion.

Secondary air injection is accomplished in the disclosed structure by causing the upwardly directed gas jet to impinge on target 48 which is of relatively open construction to provide for a secondary air injection in the usual manner. Target 48 also serves Ito deflect the llame toward the temper-alture responsive portion of thermocouple 16 which `functions las a safety device in a well known manner.

In addition to performing its normal function of secondary air injection and flame deection, target 48 is cooperatively oriented with respect to the primary air intake of the assembly which is the region designated generally 52 (FIG. 1), namely the open upper end of the space between outer member 36 and inner member 38. T-he inclination of target 48 is such that the llame is deflected to pass closely above intake region 52. This deflection is further influenced by horizontal lip 49. Two important results are achieved by the deflection of the llame in the foregoing manner.

First, the close proximity of the dame to the primary air intake opening is such that lint or dust particles which may be present in the general region of the burner must Ipass either through or in `close proximity to the pilot ame and are thus incinerated by the pilot llame so that primary yair passing downwardly through the space between outer member 36 land inner member 38 is substantially free from lint and dust particles. This incinerating action permits the pilot to maintain good flame characteristics over a longer period of time dueto a material reduction in the clogging rate `of the primary air intake.

Second, because of the proximity of the flame to the primary air intake, the iiame acts to partially restrict the primary -air intake, thereby acting with a shutter type action to contro-l the rate of primary air injection automatically in proportion to the gas pressure.

The cooperative structural relationship between target 48, lip 49 and primary air intake opening 52 is such that the pilot llame provides a self-compensationg action to control the primary air-gas mixture. The rate at which primary air is inspirated through intake 52 is in general a function of the velocity of the gas jet passing from orifice 34 into the lower end of tube 3S. When the gas jet velocity is high, primary air is inspirated through opening 52 at a greater rate, while when the gas jet velocity is low, the rate of primary air inspiraiton is in turn low. The gas jet velocity is in turn proportionalto the gas supply pressure. Thus, .at low pressures, the rate at which primary air is inspirated is relatively low, while at high gas pressures, the rate of primary air inspiration tends to be relatively high.

When the gas supply pressure is relatively low, the pilot flame is positioned quite high in hood 48 and the position of the llame at low pressure leaves the primary `air intake opening relatively free and open. As the gas supply pressure is increased, the pilot llame tends to ilow downward in the hood closer to air intake opening 52, and thus, while the primary air inspirating `action of the gas jet tends to increase the rate of primary air intake, the opening through which the primary air must pass becomes progressively restricted because of the restricting action of the pilot ila-me at primary air intake opening 52. Although greater air intake is necessary to maintain a proper mixture and a blue flame at higher pressures, the air intake increases faster proportionally than the gas flow at higher pressures with the conventional aerated pilot. This causes the hard flames and blowing experienced with the conventional aerated pilot at high pressures. Lip 49 causes a downward deflection of [the liame `at higher pressures and acts'tovshutter the air intake at these higher pressures, keeping the air intake in proportion to the increase in gas ow.

The pilot described above combines the advantages of both the incinerator or aerated pilot and the non-aerated or target type pilot and efeotively eliminates the disadvantages of both. The pilot described above may be considered as operating basically as a target type pilot which is assisted by an incinerated primary air injection. It further achieves the advantage of maintaining a relatively quiet blue ame without blowing or yellow tipping over a wide range of inlet pressures. Tests have shown that the disclosed pilot, when supplied with natural gas, maintains a quiet non-blowing, Iblue ame over a range of inlet pressure-s extending from 2 inches water column to 18 inches water column.

This exceedingly wide range of satisfactory operating pressure is due to the fact that proper mixture is not dependent entirely on either a high velocity gas jet in the target area as is the case with a pure target pilot or on a high proportion of primary air intake as is the case with the conventional i'ncineraftorv pilot. By mixing primary air with the gas during its passage through inner member 38, the jet velocity at the target is reduced, thereby reducing the tendency to blow normally present in a` pure target pilot. proportioned between primary and secondary air, a quieter, better burning flame is attainable over a much greater range of operating pressures.

The pilot hood disclosed in FIGS. 1 through 4, inclusive, is formed with a target adapted to produce a single pointed llame. The hood assembly shown in FIG. 5 is similar in construction to that of FIGS. 1 through 4 and differs from the rst described embodiment in that its hood 60 is modified in form to deflect the flame into two outwardly and upwardly divergent points by curved guide channels 62 and 64 separated from each other by a depressed central portion 66.

The hood structure of FIG, 6 differs from those disclosed in FIGS. 1 through 5 in that it isl designed to produce a three-pointed flame, the target portion 68 of the FIG. 6 hood having a pair of outwardly directed guide channels 70- and 72, and a central portion 74 which is inclined over the upper end of the inner tube to direct a portion of the gas jet upwardly through a central notch 76. The internal construction of the hoods of FIGS. 5 and 6 has not been shown in detail since it is identical to that of the hoods of FIGS. 1 through 4.

While exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is outlined in the following claims.

We claim: f

1. In combination with a source of combustion gas under pressure, orifice means connected to said source for discharging an upwardly directed jet of combustion gas from said source, and a vertically extending thermocouple assembly projecting upwardly at the front side of said orice means in spaced relationship therewith; the

As 4the air injection is more evenly 5 improvement comprising a combination incinerator-target type pilot burner hood assembly comprising a first Ver' tieally disposed open ended tubular member, means on the lower end of said first tubular member for mounting said first tubular member upon said orifice means at a location such that a jet of combustion gas discharged upwardly from said orifice means passes upwardly and centrally through said rst tubular member, a target mounted at the upper end of said first member and inclined upwardly and forwardly from the rearward side of said first tubular member to overlie the opening at the upper end of said first tubular member and to dene a relatively open region above said rst tubular member for the injection of secondary air to mix with combustion gas above said first tubular member, a second vertically disposed open ended tubular member mounted within `said rst tubular member to deline an annular passage between the inner Wall of said first tubular member and the outer wall o said second tubular member, the upper end of said second tubular member being located at substantially the same level as the upper end of said rst tubular member and the lower end of said second tubular member being spaced upwardly from the lower end of said first tubular member, said second tubular member being related to said mounting means in a fashion such that a gas jet discharged from said orifice means passes upwardly through said second tubular member to thereby inspirate a flow of air downwardly through the annular passage between said tubular members for mixture with the jet of gas at the lower end of said second tubular member, said second tubular member being offset rearwardly within said rst tubular member whereby the radial width of said annular passage is greatest adjacent the forward side of said assembly, and said target being positioned to deliect a pilot flame .at the upper end of said second tubular member laterally across the forward portion of the upper end of said annular passage into operative relationships with said thermocouple assembly and to at least partially restrict the ow of air inspirated through said passage while at the same time defining the upper boundary of said region for the injection of secondary air into the primary aircombustion gas mixture discharged from the upper end of said second tubular member.

2. Apparatus as defined in claim 1 wherein said tubular members and said target are formed. from a unitary piece of sheet material, said second tubular member being supported within said first tubular member by a radially extending vertical web.

References Cited in the le of this patent UNITED STATES PATENTS 2,920,126 Hajny Jan. 5, 1960 2,959,216 Alger Nov. 8, 1960 3,002,554 Biggle Oct. 3, 1961 3,048,216 Kile Aug. 7, 1962 FOREIGN PATENTS 4,931 Great Britain of 1905 70,193 Sweden Oct. 1, 192,7 

1. IN COMBINATION WITH A SOURCE OF COMBUSTION GAS UNDER PRESSURE, ORIFICE MEANS CONNECTED TO SAID SOURCE FOR DISCHARGING AN UPWARDLY DIRECTED JET OF COMBUSTION GAS FROM SAID SOURCE, AND A VERTICALLY EXTENDING THERMOCOUPLE ASSEMBLY PROJECTING UPWARDLY AT THE FRONT SIDE OF SAID ORIFICE MEANS IN SPACED RELATIONSHIP THEREWITH; THE IMPROVEMENT COMPRISING A COMBINATION INCINERATOR-TARGET TYPE PILOT BURNER HOOD ASSEMBLY COMPRISING A FIRST VERTICALLY DISPOSED OPEN ENDED TUBULAR MEMBER, MEANS ON THE LOWER END OF SAID FIRST TUBULAR MEMBER FOR MOUNTING SAID FIRST TUBULAR MEMBER UPON SAID ORIFICE MEANS AT A LOCATION SUCH THAT A JET OF COMBUSTION GAS DISCHARGED UPWARDLY FROM SAID ORIFICE MEANS PASSES UPWARDLY AND CENTRALLY THROUGH SAID FIRST TUBULAR MEMBER, A TARGET MOUNTED AT THE UPPER END OF SAID FIRST MEMBER AND INCLINED UPWARDLY AND FORWARDLY FROM THE REARWARD SIDE OF SAID FIRST TUBULAR MEMBER TO OVERLIE THE OPENING AT THE UPPER END OF SAID FIRST TUBULAR MEMBER AND TO DEFINE A RELATIVELY OPEN REGION ABOVE SAID FIRST TUBULAR MEMBER FOR THE INJECTION OF SECONDARY AIR TO MIX WITH COMBUSTION GAS ABOVE SAID FIRST TUBULAR MEMBER, A SECOND VERTICALLY DISPOSED OPEN ENDED TUBULAR MEMBER MOUNTED WITHIN SAID FIRST TUBULAR MEMBER TO DEFINE AN ANNULAR PASSAGE BETWEEN THE INNER WALL OF SAID FIRST TUBULAR MEMBER AND THE OUTER WALL OF SAID SECOND TUBULAR MEMBER, THE UPPER END OF SAID SECOND TUBULAR MEMBER BEING LOCATED AT SUBSTANTIALLY THE SAME LEVEL AS THE UPPER END OF SAID FIRST TUBULAR MEMBER AND THE LOWER END OF SAID SECOND TUBULAR MEMBER BEING SPACED UPWARDLY FROM THE LOWER END OF SAID FIRST TUBULAR MEMBER, SAID SECOND TUBULAR MEMBER BEING RELATED TO SAID MOUNTING MEANS IN A FASHION SUCH THAT A GAS JET DISCHARGED FROM SAID ORIFICE MEANS PASSES UPWARDLY THROUGH SAID SECOND TUBULAR MEMBER TO THEREBY INSPIRATE A FLOW OF AIR DOWNWARDLY THROUGH THE ANNULAR PASSAGE BETWEEN SAID TUBULAR MEMBERS FOR MIXTURE WITH THE JET OF GAS AT THE LOWER END OF SAID SECOND TUBULAR MEMBER, SAID SECOND TUBULAR MEMBER BEING OFFSET REARWARDLY WITHIN SAID FIRST TUBULAR MEMBER WHEREBY THE RADIAL WIDTH OF SAID ANNULAR PASSAGE IS GREATEST ADJACENT THE FORWARD SIDE OF SAID ASSEMBLY, AND SAID TARGET BEING POSITIONED TO DEFLECT A PILOT FLAME AT THE UPPER END OF SAID SECOND TUBULAR MEMBER LATERALLY ACROSS THE FORWARD PORTION OF THE UPPER END OF SAID ANNULAR PASSAGE INTO OPERATIVE RELATIONSHIPS WITH SAID THERMOCOUPLE ASSEMBLY AND TO AT LEAST PARTIALLY RESTRICT THE FLOW OF AIR INSPIRATED THROUGH SAID PASSAGE WHILE AT THE SAME TIME DEFINING THE UPPER BOUNDARY OF SAID REGION FOR THE INJECTION OF SECONDARY AIR INTO THE PRIMARY AIR-COMBUSTION GAS MIXTURE DISCHARGED FROM THE UPPER END OF SAID SECOND TUBULAR MEMBER. 